Boiler Losing Pressure - Isolation Valve Oddness...

[shadowboxer]

I was hoping someone could give some advice about our problem.

2 weeks ago, our Valliant boiler started losing pressure, approximately 1 bar every day. I switched it off and isolated the return and flow using the valves underneath the boiler, but the pressure kept dropping at the same rate. Hence the assumption was boiler problem, not system leak.

We've got BG boiler cover, so gave them a call. They isolated the boiler the same way to double check - boiler still losing pressure. So they investigated further - bags placed over condensate and pressure relief pipe to catch water (nothing there). They found water inside a container in the boiler - this led to them replacing the heat exchanger. But pressure still dropping (same rate).

So, boiler completely disconnected and capped off (return and flow, mains supply and hot and cold feeds, but not gas supply). Pressure held perfectly.

Before reconnecting, the expansion vessel was noted to be quite flat, so this was pumped (but they stated this was unrelated as pressure was not rising with heating on).

Boiler now reconnected, but is still losing pressure.

So, BG say it's a system leak. Okay, but why is there pressure loss in the boiler when we use the isolation valves under the boiler? BG say those valves definitely hold water as they were used when disconnecting the boiler - however BG suggest that they 'can hold water, but perhaps not pressure'. That doesn't makes sense to me

Before we start ripping up flooring looking for a leak, can anything think of a reason that may have been overlooked? Is it possible for the isolation valves to 'not hold pressure' but happily 'hold water'? Is there 'something' different when using isolation valves compared to completely disconnecting and capping off return and flow pipes?

Any thoughts, however obscure, would be much appreciated!

 

[I Like Sleeping]

Try leaving flow and return on and leave cold feed to boiler off. See what happens.

 

[ianmcd]

WOW you seem to have a real problem on your hands, it sounds though that your BG engineer actually knows what he is talking about as he has done everything right, it sounds as though your isolating valves are weeping under pressure so the seperation test gives false results some prat on here will tell you to install leak sealer dont do it you will damage your boiler and it doesnt work its absolute crap, finding where the pressure drop is coming from can be extremely difficult, losing 1 bar can be as little as half a cup of water, it is worth while putting a bag over the drain point outside if you have one they can leak too, does it always lose pressure at the same rate ? or is it different if you have the heating on or off ?

 

[shadowboxer]

Try leaving flow and return on and leave cold feed to boiler off. See what happens.

If the pressure then remains constant, what problem would this suggest?

finding where the pressure drop is coming from can be extremely difficult, losing 1 bar can be as little as half a cup of water, it is worth while putting a bag over the drain point outside if you have one they can leak too, does it always lose pressure at the same rate ? or is it different if you have the heating on or off ?

Engineer reckons on our system, 1 bar will be approx half a litre, so I think we'd notice wet patches in the ceiling if it was anywhere other than ground floor.

All external 'orifices' have been bagged and checked - no water.

One room in the ground floor is glued tongue and groove oak, so massive PITA if that's to come up - that said, that room has its own isolation valves so we isolated last week and the pressure still dropped - of course, with BG insisting isolation valves can still leak pressure, they reckon we're better off completely capping that room off.

Pressure drop is actually a bit slower since reconnection, although as is typical for us after a drain down, one room isn't heating and needs rebalancing (same room with the oak flooring) - rads are fully filled just not heating, don't know if this is related. However this room has been like that since it was set up over a year ago so it's not a sudden occurrence like the pressure drop.

The main thing at this point is to understand why the isolation valves appear not to work for pressure, but can still hold water. Surely the water IS the pressure? Could it be air escaping through the valve?

The system water is very brown BTW, even after several drain downs - we have a magnacleaner, but no inhibitor ATM due to the constant drain downs over the past couple of weeks and not entirely sure what the inhibitor status was beforehand. Could system corrosion be causing increased air and therefore leading to isolation valve 'air' leaks? Clutching at straws here.

 

[ianmcd]

have you had any work done on the ground floor in say the last 12 months ? I have come accross situations where carpets have been replaced and a nail or screw from the threshold bar want through a water pipe but sealed and about 6 months later started to corrode and started leaking would it be possible to isolate the downstairs circuit and see if the pressure still drops ?

 

[picasso]

I would disconnect the filling loop and see if the system pressure stabalises

 

[shadowboxer]

Rennovation job, so lots of work. That entire kitchen diner was re-piped, new rads, oak floor down, just over a year ago. Most of it is not accessible as the cellar only covers a bit of the ground floor.

I will cap off that entire circuit, it's not hard to do from the cellar where it tees off.

But do want to rule out anything obvious with te boiler first - those valves are doing my head in.

 

[ianmcd]

as you posted that boiler held pressure when capped off and PRV had a bag over to prove no discharge then I think you can trust that the boiler is OK, think all you can do now is cut and cap off sections of your system one at a time to find out which section is causing the pressure loss sorry I cant give you an easy fix its a matter of elimination now could be a nail or similar through a pipe or a faulty joint, once you have found the problem clean the system and add inhibitor as constant re filling will have caused damage and your water content will be poor

 

[picasso]

Has anyone checked that the prv pipe is in one piece through the wall ? you could have a drip in the wall and never see it.

 

[ianmcd]

you could try instead of capping off the boiler just make a simple loop between the flow and return with a section of PE or copper pipe and fire the boiler and see if it loses pressure this will rule out any doubts about expansion PRV heat exchanger etc but as I said earlier it seems that the BG engineer knows what he is talking about and I think you have a leak on your system

 

[shadowboxer]

Has anyone checked that the prv pipe is in one piece through the wall ? you could have a drip in the wall and never see it.

When the boiler was disconnected from the system, the pressure was stable - so surely the prv pipe would have to be fine?

 

[shadowboxer]

I'm going to begin capping off sections tomorrow and monday, but before I do, can anyone confirm whether or not it's a known issue that isolation valves can sometimes hold water but not pressure? Basically everything I've read says that isolating via those valves is a sound test, but BG saying the opposite.

Also someone mentioned turning off the incoming water feed - can you explain what the reasoning is behind this? I ask, because this was disconnected during the tests, but it was reconnected at the same time as the hot/cold pipes, so no independent test was carried out just with this. But how could this negatively affect system pressure?

 

[picasso]

The isolating valves can be a bit hit and miss, they might completly seal for one test and let by the next time you use them, the nrv for the system could be passing and if the pressure in the mains is low enough the boiler pressure will backfeed, bit of a long shot as I reckon the leak is on your system.

 

[shadowboxer]

The isolating valves can be a bit hit and miss, they might completly seal for one test and let by the next time you use them, the nrv for the system could be passing and if the pressure in the mains is low enough the boiler pressure will backfeed, bit of a long shot as I reckon the leak is on your system.

Thanks - the mains pressure is pretty high in our property, so would assume it wouldn't be this, but it's odd all round ATM, so maybe!

But yes I agree, it's most likely a system leak, but I just can't get past the iso valves not working for 'pressure' but working to hold back water - I've spoken to a Valliant engineer on another forum and he reckons he's never seen one of the valliant iso valves fail. So it's a bit of a mystery.

 

[Whitespirit66]

Has anyone tried a hydraulic pressure tester on the flow and return pipes at the boiler for the ch system?

If this proves a leak in the rads or pipes, then instead of capping off sections of the system, you can use the pressure tester to test these sections individually to locate leak.